1. Field of the Invention
The present invention generally relates to a gas-insulated bushing having a capacitor unit, as used in high-voltage equipment, and more particularly is concerned with a gas-insulated bushing of the type including an insulating tube filled with an insulating medium, a central conductor centrally arranged within the insulating tube and a capacitor unit connected to the central conductor and partitioning the interior of the insulating tube.
2. Description of the Prior Art
SF.sub.6 (sulfur hexafluoride) gas-insulated bushings are now used for many types of high voltage equipment and it is anticipated that such gas bushings will also be used in UHV (Ultra High Voltage) power transmission. However, with ultra-high voltages, control of the electrical field is an important problem, and gas-insulated bushings of the stress-cone type have therefore made their appearance. In such a bushing, the electrical field is relieved by arranging a capacitor unit on the central conductor of the bushing. The capacitor unit partitions the interior of the bushing into a high-pressure region and a low-pressure region, so that the high internal gas pressure does not directly act on the external insulating tube.
FIG. 1 shows the structure of a prior art stress-cone bushing (g). A central conductor b is provided in the center of insulating tube a. On the central conductor b and concentrically therewith is arranged a capacitor unit c having a stepped cylindrical configuration. The capacitor unit c relieves the electrical field within the bushing and partitions the gas into a high-pressure region within capacitor unit c and a low-pressure region between capacitor unit c and the insulating tube a.
A cooling case e at the top of insulating tube a is connected to the central conductor b and removes heat within the bushing. A shield ring f is also located at the top of insulating tube a to relieve the electrical field in the upper region of the bushing. The bushing g constructed as above described is supplied for use fixed to a tube base h by bolts i. In the above structure, the portion which connects central conductor b and capacitor unit c and which projects sharply from central conductor b is necessarily large. Because of the concentration of the electric field j as shown in FIG. 2 and the consequential risk of insulation breakdown, insulating tube a is required to have considerable size.